Rheostat



Nov. 1, 1932. F. H. BULLMGER RHEOSTAT Filed June 21. 1930 Patented Nov.,1, 1932 UNITED STATES FREDERIC H. BULLINGER, OF BRONXVILLE,

NEW YORK, ASSIGNOR TO WARD LEONARD ELECTRIC COMPANY, A, CORPORATION OF NEW YORK BHEOSTAT Application filed June 21;

This invention relates to an improved form of construction of rheostats and tothe method of making rheostats.

The invention particularly relates to that form of rheostat in which a movable contact arm passes over and makes successive engagement with a series of contacts to which a resistive conductor is connected.

One object of the present invention is to 0 provide an improved contact between the resistive conductor and the fixed contacts of the rheostat which will insure good electrical connection between the parts, and also be permanent and unaffected in the course of manufacture when subjected to the insulating and enameling process such as occurs during the manufacture of the usual enameled plate rheostats. Another object is to permit the convenient use of fixed contacts of rectangular shape, as distinguished from the usual round form of contact buttons, the rectangular form being preferable, particularly for heavy-duty rheostats, where a comparatively large contact surface is necessary and where economy in space is desirable. Another object is to provide means for insuring proper position of the fixed contacts of the rheostat and the maintaining of such position and of the resistive conductors during the insulating and enameling process. Hcretofore, it has been a matter of considerable difliculty and expense in properly positioning the fixed contacts and resistive conductor in this type of rheostat, not only during the preparation of the same for the firing, but also during the vitrifying of the enamel material in the baking,-or firing, operation. Even though great care be taken in properly positioning the parts before firing and'in introduction to the firing 4o furnace, the heating often causes the parts to shift their relative positions, due to the annealing and relief of strains, so that when the enameled plate is withdrawn from the furnace, it is not infrequently found that the 4 contacts and resistive conductor have shifted 1930. Serial 1T0. 462,754.

their positions sufliciently to cause electrical connection between adjoining sections, giving short-circuit connections and necessitatin in some instances, the loss and discarding of the device. By the present invention, the parts are not only securely maintained in fixed position before the firing operation, but their fixed relative positionis insured by auxiliary means provided for that purpose during the firing operation. in cost of manufacture, the securing of uniformity in production, the avoiding of rejec tions and the production of a permanently dependable and durable product.

The invention will be understood by reference to the following description and accompanying drawing in which: Fig. 1 is a front view of one form of rheostat embodying the invention, part of the insulating material being indicated as broken away to reveal the resistive conductors in their relation to the fixed contacts; Fig. 2 is a front view of one-form of improved contacts before connection to the resistive conductor and before assembling; Fig. 3 is a side view thereof; Fig. 4 is a back view thereof; Fig. 5 is a perspective view showing one form of resistive conductor prepared for union withthe fixed contacts and Other objects include a reduction also showing two of the fixed contacts secured conductor 4 indicated by dotted lines and carried by the rotatable arm 5 of the rheostat. The terminals 6 are indicated as being connected to opposite fixed contacts, so that when the arm is rotated, more or less of the resistive conductors 7 will be included in the circuit. The resistive conductors and base of thereto, it may be made in any'suitable form for the particular purpose desired.

My improved form of contact shown in Figs. 2, 3, and 4, is of general rectangular form and has projecting portions 3a at the ends of. its base which are adapted to be covered by the insulating coating 8, so as to assist in securely and firmly holding the fixed contacts in position on the supporting plate after completion of the rheostat. In the bottom of the contact is a slot 31) extending lengthwise thereof and extending well into the body of the contact. The sides of the contact are bulged outwardly as shown at 30, in the region of the slot. The contact is provided, in the particularform shown, with a pair of projecting lips 3d at the front surface thereof near the center and extending cross-wise to the face of the contact.

Referring to Fig. 5, the resistive conductor 7 is shown looped back-and-forth upon itself in order to give the required resistance be tween contacts, and at its outer portion is bent to return for connection with the next contact from which it passes inwardly and is again bent to return for connection with the succeeding contact. In some cases, the resistive conductor may be located on one side jonly of. the contacts, in which case the con doctor is bent at the contact to extend outwardly from the same portion at which it Joined the contact. At the portions of the resistive conductor where it is to be connected to the contacts, the conductor is looped outwardly as shown at 9 in Fig. 5, for the purpose of providing means for connection to the fixed contacts. According to the meth d of assembly, the resistive conductor is loopid as already described and then the contacts 3 are successively added to theloops 9 of the resistive conductor by causing these loops to pro ect within the slots 36. The sides 30 of the contacts are then firmly compressed toward the loop portions 9 of the resistive conductor, so as to cause the metal of, the contacts to firmly grip, surround and embed the loops 9, so that when the contacts are thus united with the resistive conductor, the bulging sides 30 of the contacts are forced inwardly to such an extent around the loops 9 that the sides of thecontacts have inwardly depressed portions as indicated at 3e, instead of outwardly bulging portions. This compression may, of course, be conveniently accomplished by an automatic compressor,which will cause the union of the contacts with the resistive conductor in rapid succession.

When all of the required number of fixed contacts are united with the resistive conductor to form the complete set necessary for the rheostat, the parts are then assembled in their final position by means as shown in Fig. 6. Here a circular element 10, in this instance an iron or steel wire, is provided for securely holding the contacts in place. The contacts are united with the element 10 and positioned in circular form under the same by means of the lips 3d of the contacts embracing the circular element. 'The contacts are positioned in proper relation to each other on the circular element 10 and then pressure is applied to the lips 3d, so as to cause them to firmly grip the wire 10, as by forcing thelips toward each other, or by compression against the wire. When the contacts are thus held in their final and relative positions, the resistive conductor may be then properly bent and placed in an oven, or otherwise bakedor dried, to form the insulating protective coating, but a vitreous enamel coating is far preferable to other materials, owing to its high insulating qualities, imperviousness to moisture, and durability.

After removal from the furnace, the retaining element 10 is removed from the fixed contacts, as by pulling it outwardly from the face of the contacts, or by cutting it out; and then the lips 8d and surfaces'of the fixed contacts are ground down, or milled, so as to lie in the same plane and present smooth and even surfaces for engagement with the movable contact, or contacts of the rheostat arm.

The movable contact arm is then secured to the rheostat plate in any of the usual known ways, which completes the assembly of the rheostat.

, It is evident that this invention permits the convenient use of rectangular contacts, and it has been demonstrated that my improved form of connection between the resistive conductor and the fixed contacts gives an excelcontact may be slotted b cutting a groove across it, or lengthwise it, and having the projection or loop in the resistive conductor,

or a portion of the conductor, extend into this slot and then the two sides pressed together, or folded over the resistive conductor, so as to partially, or wholly, embed the same to form a permanent electrical contact.

. Instead of using a ring or wire secured to the faces of the contacts by projecting lips as described, for positioning them, the circular element might be otherwise secured, as by use of a ring brazed to the surface of the contacts. In some cases, I have soldered the circular element tothe contacts, and although the solder may melt during the enameling process, yet distortion of the parts" is prevented before melting of the solder, so that satisfactory results have been obtained by this means. The retaining means has also been accomplished by first forming an integral ring of brass, or other material, and forming the contacts by slotting the ring on the rear side, so as to form a series of fixed contacts held together and retained in proper position by the portion of the uncut material which is left at the face of the contacts in the form of a continuous ring. This, of course, is turned or ground off after the firing of the enamel.

Although I have described a preferred em-' bodiment of this invention, it is evident that various modifications may be made and the method modified, without departing from the scope thereof; and where I have referred in the claims to maturing the insulating coating, it is to be understood that this applies to any form of insulating coating and to the drying, setting, baking, firing, or the like, of the coatmg.

Iclaim: 1. A rheostat comprising an insulating support, a resistive conductor on said support, fixed contacts on said support, said contacts having openings on their inner ends and extending lengthwise towards the faces thereof receiving and compressing portions of said conductor, and an insulating coating covering said conductor and embedding the inner ends of, said contacts. I

2. A rheostat comprising an insulating support, a resistive conductor, said conductor having outwardly projecting portions, fixed contacts on said support, said contacts being of rectangular form and'having openings on their inner ends extending lengthwise and towards the faces thereof recelvlng and compressing said projecting portions, and an insulating coating covering said conductor and embedding the inner ends of said contacts.

3. A rheostat comprising an insulating support, a resistive conductor, said conductor having outwardly projecting looped portions, fixed contacts on said support,said

contacts being of rectangular form and having openings on their inner ends extending lengthwise and towards the faces thereof receiving said looped portions and the walls of said openings being compressed inwardly and compressing said looped portions, and an insulating coating covering said conductor and embedding the inner ends of said contacts.

4. The method of making a rheostat which comprises forming openings in the inner ends of the contacts and extending lengthwise towards the faces thereof, forming the resistive conductor to have portions entering said openings, and compressing the sides of said contacts to cause the walls of said openings to engage said portions.

5. The method of making a rheostat which comprises forming openings in the inner ends of the contacts and extending lengthwise to'-' wards the. faces thereof, forming the resistive conductor to have outwardly projecting portions entering said openings, and compressing the sides of said contacts to cause opposite sides of said openings to engage said portions.

6. The method of making a rheostat which comprises forming the contactspf rectangular shape and with openings at their inner ends extendin lengthwise and towards the faces thereof, orming the resistive conductor to have outwardly projecting portions entering said openings,.and compressing the side walls of said contacts to clamp said portions between them.

7. The method of making a rheostat having a series of contactsconnected to a resistive' conductor which comprises uniting with the outer portions of said. contacts a positioning element, applying the contacts and conductor to their support, applying an insulating coating over the resistive conductor and around the bases of the contacts, maturin said coatin and then removing said positioning eleme" t.

8. The method of making a rheostat having a series, of contacts connected to a resistive conductor which comprises forming a series of openings in the outer portions of said contacts, placing a positioning element in said openings, applying the contacts and conductor to their support, applying an insulating coating over the resistive conductor and around the bases of the contacts, maturing said coating, and then removing said positioning element.

9. The method of making a rheostat having a series of contacts connected to a resistive conductor which comprises forming said contacts with projecting port-ions at the outer portions thereof, causing said projecting portions to engage a positioning element, applying the contacts and conductor to their support, applying an insulating coating over the resistive conductor and around the bases of iii 4 1,see;oso

around the bases of. the contacts, maturing ing coating over the resistive conductor and said coating, and then removing the mechanical connection from the outer portions of p 1 said contacts. Y

, FREDERIC H. BULLINGER. 

